In the preceding few years both the number and quality of heat flow measurements have increased dramatically, and, except for the explosion aboard the Apollo 13 spacecraft, we might be able to report the first extraterrestrial heat-flow measurement [see Langseth et al., 1970].
Between 1965 and August 1969, the number of heat flow measurements increased from 1044 to 3564 [Von Herzen and Lee, 1969; Lee, 1970], and new measurements were appearing at the rate of 600 per year. These figures are for all available data, but the proportional increase in activity in this field by investigators from the United States is at least comparable. Even with twice the data, Von Herzen and Lee found no significant changes in selected averages reported by Lee and Uyeda . A recent tabulation of heat flow data was published by Simmons and Horai  and the same authors [Horai and Simmons, 1969b] presented spherical harmonic analysis maps of heat flow.